Sheet feeder units are used in conjunction with suction head units in order to control the flow of sheets through a printing machine. Normally, sheets are removed individually from a sheet pile and fed to a belt table. The sheets are then conveyed by the belt table to a sheet-processing machine.
In known sheet feeder units of this type, as disclosed in the German Patent, DE 41 40 051 A1, the suction head unit and the belt table are driven in phase with the sheet-processing machine. Through this means, the flow of sheets through the printing machine may be better controlled so that the sheets are always transferred to the sheet-processing machine at precisely the right time.
Problems in sheet feeders units stem from processing different types of sheets. Depending on the quality and surface finish of the sheets, a varying slip can occur between the sheets and the transporting belts of the belt table. The result is that the sheets are not transferred to the sheet-processing machine at the right time (i.e. the actual time of the sheet transfer deviates from the reference time).
Further, problems in sheet feeders stem from disruption when the sheet is transferred to the belt table. Disruption occurs when the transferred sheet strikes at high speed the front lays of the belt table which define the transfer position. The transferred sheet then bounces back away from the belt table. If the sheet does bounce back upon impact with the belt table, the sheet is no longer being fed to the sheet-processing machine in a precisely positioned manner, causing errors in the sheet feeding.